1. Field of the Invention
The present invention relates to an amorphous material which is suitable for a regenerator of the refrigerator due to its good mechanical properties and thermal properties.
2. Description of the Prior Art
Miniature-sized refrigerator are now in general use for the vacuum equipment employed in the production of semiconductors by ion implantation or sputtering. They fall into two main groups: those equipped with a regenerator and those equipped with a heat exchanger. Those belonging to the first group, which are based on the Gifford-McMahon cycle or Stirling cycle, are commonly used for refrigeration at liquid nitrogen temperatures or liquid hydrogen temperatures due to their simple structure and high reliability.
The material packed in the regenerator of the refrigerator is required to have a large specific heat capacity and good thermal conductivity in the range of operating temperatures. In the past, copper, lead and alloys thereof have been used as a regenerator material. They have a disadvantage of rapidly decreasing in specific heat capacity at 20.degree. K. or below, which presents difficulties in producing very low temperatures in that range.
To solve this problem, there has been proposed a rare earth alloy as the regenerator material which has an anomalous heat capacity due to magnetic phase transition (Japanese Patent Publication No. 30473/1977). Improvements on it have also been disclosed (Japanese Patent Laid-open Nos. 310269/1989 and 1050/1991).
The conventional rare earth alloy used as the regenerator material is an intermetallic compound having a low mechanical strength. In other words, it is too brittle to be formed into a foil or coil. Therefore, it is used mostly in the form of fine powder with a particle diameter of 10 .mu.m-1 mm. Fine powders of rare earth alloy need great care in handling because of extremely high chemical activity. In addition, excessively fine powder increases resistance to the flow of the working fluid and escapes from the net containing it.